The Chinese calendar combines the lunar and solar
systems together. The Year and Day cycles use the solar
system. However, there are two different Month cycles in the Chinese calendar. One
uses the lunar system and the other uses the solar system. In the lunar system of Month, the new
moon day is the first day of a lunar month. The length of a lunar month is the length of time
between two new moon days. The name of a lunar Month is taken from
the solar system. The Chinese solar months are not like the months of a
modern calendar. The Chinese calendar divides the year into 24
solar
segments according to the sun positions on the tropical zodiac (Similar to western astrology).
Each segment's name was given for ancient Chinese farmers' use. To understand the whole picture view
the following chart.

Solar Segment

Sun Longitude

Month Name

Astrology
Name

Start of Spring

315

1 -
Tiger

Aquarius

Rain Water

330

Pisces

Excited Insects

345

2 -
Rabbit

Vernal Equinox

0

Aries

Clear and Bright

15

3 -
Dragon

Grain Rains

30

Taurus

Start of Summer

45

4 -
Snake

Grain Fills

60

Gemini

Grain in Ear

75

5 -
Horse

Summer solstice

90

Cancer

Slight Heat

105

6 -
Sheep

Great Heat

120

Leo

Start of Autumn

135

7 -
Monkey

Still Hot

150

Virgo

White Dew

165

8 -
Chicken

Autumnal Equinox

180

Libra

Cold Dew

195

9 -
Dog

Frost Descends

210

Scorpio

Start of Winter

225

10 -
Pig

Light Snow

240

Sagittarius

Heavy Snow

255

11 -
Rat

Winter Solstice

270

Capricorn

Little Cold

285

12 -
Cow

Severe Cold

300

Aquarius

The solar months are defined by the sun
longitudes. The first month, Tiger month, begins from the Start of
Spring segment or when the sun enters the 315th degree on the tropical zodiac. The second
month, Rabbit month, begins from the Excited Insects segment or
when the sun enters 345th degree. The beginning of a solar month is called the
Segment Point. In the middle of a solar month is called the
Center
Point. For example, the segments of Rain Water and
Vernal
Equinox are Center Points. The astrology names of Pisces and
Aries apply to these Center Points.

The lunar month name is derived from the Solar
Center Point. For example, If a lunar month contains the Rain Water Center
Point, then it is the first month of the lunar calendar, as known as the Tiger month.

If a lunar month does not
contain any Solar Center Point, that month is known as a Leap Month. The
name of this leap month is the same as previous lunar month. The reason to assign leap
months is that we want the moon cycle to harmonize with the sun cycle. Because one year has
about 365.2425 days and one month has about 29.53 days, one year has about 12.3685 months.
12.3685 is about 12 and 7/19. If we put seven extra months in 19 years, sun and moon
should be back to the same sky position. "Seven Leap Months in 19 years" is easy
for people to remember. However, 12.3685 is almost equal to 12 and 144/391. That
means "144 Leap months in 391 years" is a more accurate way to assign Leap months.
So far, no one has lived long enough to observe the entire cycle.

Anyway, the principles of the Chinese Calendar use
the following four rules which the ancient Chinese made them thousand years ago.

The new moon day is the first day of a lunar month

The name of a lunar name is named by the Solar Center Point

The first lunar month of the year is the
Tiger month, which contains Rain
Water center point

The lunar month without a Center Point is a Leap month( Intercalary Month )

In the Chinese Lunar Calendar, the new moon day
is the first day of a lunar month and the length of a lunar month is the length between
two new moon days. In the Chinese Fortune-Telling (Astrology)
Calendar, the first day of a month is the day on a Solar Segment Point
and the length of a month is the length between two Solar Segment Points. Therefore there
is no Leap Month in the Chinese Fortune-Telling System.

Without this knowledge, above-mentioned, most people
will be confused about the solar months and lunar months. They may think all Chinese
Fortune-Telling system use lunar months. Actually, the Fortune-Telling system called
Eight Characters only uses the solar month, not the lunar month. The other popular
system called Dipper uses solar month and lunar month together.

The counting system of Day is the Stem-Branch 60-day cycle system. No one knows who invented the
Stem-Branch for Day counting system, but legend has it that characters of Day Stem-Branch were found on Oracle bones. The Animal names of Stem-Branch were applied into
the Month system around 206 B.C. (between the
Chin and Han dynasties). The Stem-Branch was applied into
the Year system around 164 B.C..

Almost every Chinese dynasty had its own
calendar. One reason was that the new emperor needed to announce the new rules including the
new calendar to the public. The other reason was that the astronomer's officers had to make some
adjustments on the calendar in order to match the sun and moon in the sky.

The first day of a year has been changed many
times in Chinese calendars. The current Chinese calendar uses the first day of the first
month of Tiger month as the first day of a year, which was initially adopted by the
Shiah dynasty
(2183-1752 B.C.). Today, some people consider the Winter Solstice as the first day of a
year in the Chinese Fortune-Telling System, because that makes more sense from the
astronomy view.

The Chinese Lunar Calendar system is
not perfect, because the length of solar month is not always greater than the
length of a lunar month. As a result, a lunar month might contain two solar
Center Points. Those months are found in the winter of 1548, 1680, 1700, 1719,
2053, 2072 and so on. This imperfection causes the trouble in the assignments of
the Chinese Lunar Leap Month. That's why there is no
simple formula for Chinese Lunar Calendar conversion.